Contractor: UC Davis

Contract Number: 03-346

This report describes the design, development, fabrication and testing for primary functionality of an integrated prototype of a small footprint particle size sampler, the MicroAPA. The new instrument consists∑ of a custom designed and fabricatecf MEMS based ionizer and mini-DMA (separator electrodes), custom designed electrometer and Faraday's cup, as well as off-the-shelf components.

The MEMS based corona ionizer and mini-DMA were constructed using microfabrication techniques. This allows a corona pin diameter of 20um to be easily achieved at a very low cost. It also permits the corona pin to be accurately positioned between two miniature copper grids 4mm apart. By using a high voltage but low current power source, a steady corona discharge is achieved at very low power consumption (less than 20mW). In-lab experiments show that the MEMS based corona ionizer and miniDMA are able to adequately sort particles ranging from 30nm to 300nm (with the size distribution limited by the TSI constant output atomizer capabilities, which is 30nm to 300nm).

A custom designed electrometer circuit has also been developed by a vendor for the MicroAPA project. The electrometer has a gain of 1VIpA with the baseline voltage at 250mV. A custom designed Faraday's cup consisting of a detection cup nested within shielding cup was also designed and fabricated by the MicroAPA study team. The detection cup captures incoming charged nanoparticles and relays the electrical current to the electrometer.

System integration was based on a super-PLC controller as the main platform. The board controls all data relay and acquisition as well as power management and components algorithms. The integrated prototype was successfully tested in a laboratory environment using an atomizer as the nanoparticle source. It has also been deployed in a controlled roadside environment. These results, while encouraging also suggest that additional modifications to the Faraday's cup are necessary.

In summary, the current instrument specifications and testing show that the prototype instrument design will perform acceptably in protected, indoor environments and with its current chassis, in conditions that range from 40-100 degrees F and RH less than 90 (California weather). For sampling of stacks under high temperature conditions, additional experimentation would be required.